Variable iris using charged opaque particles

Abstract

Variable iris using charged opaque particles The present invention relates to a variable iris using charged opaque particles, and to a method for operating such a variable iris.According to the invention, the variable iris has a first transparent substrate and a second transparent substrate, which are separated by one or more ribs to form a cell confining charged opaque particles, the first transparent substrate being provided with at least a first electrode and a second electrode both being adapted to be connected to a voltage source for acting on the charged opaque particles, and at least a third electrode adapted to be connected to the voltage source for acting on the charged opaque particles, the voltages applied to the first electrode, the second electrode, and the third electrode being controllable to have the same or opposite signs. The variable iris further has a pulse driver for applying voltage pulses to the electrodes.

Description

FIELD OF THE INVENTION[0001]The present invention relates to a variable iris using charged opaque particles, and to a method for controlling such a variable iris.BACKGROUND OF THE INVENTION[0002]Nowadays lots of digital (still and movie) cameras are available on the market. Different kinds of diaphragms for controlling the amount of light falling onto a photodetector are utilized in lens optics. The most widely used diaphragm is the iris diaphragm. However, this mechanical iris diaphragm has a number of disadvantages. It is not suitable for small lens assemblies, as for example in current small digital cameras, due to the necessary size of the mechanical components. In addition, it is not possible to control the shape of the aperture. As springs and a mechanical movement are used, the iris diaphragm needs maintenance. Finally, this type of diaphragm has a relatively slow response.[0003]To circumvent at least some of the above problems, electronic diaphragms based on liquid crystal e...

AI Technical Summary

Benefits of technology

[0008]The voltage applied to the third electrode, which is located on the second transparent substrate or on the rib, supports the movement of the charged opaque particles away from the first or second electrode and into the inside of the cell. As both the first and the third electrode are used for setting the variable iris to a fully open state, the response of the iris is very fast, i.e. the iris aperture changes rapidly. This makes it possible to use the variable iris even in camcorder optics. The variable iris according to the invention has a plurality of further advantages. Due to the omission of mechanical actuators the iris can easily be miniaturized. It is, therefore, suitable for small image capturing devices. In addition, the shape of the aperture is maintained even if the size of the open aperture is very small. In contrast, for mechanical iris diaphragms the shape of the aperture is distorted if the size of the open aperture is very small, which leads to a change of the blur pattern. A further advantage is the possibility to achieve any shape of the iris aperture, including a polygonal aperture and a ring-type aperture.

[0009]Recently electrophoretic particles having a memory effect have been developed. For example, in “SID '04 (Society for Information Display), Digest of technical papers”, pp 133-135 a “Quick response liquid powder display” is disclosed. The particles used for this display have a diameter of less than 10 μm, the response time is less than 0.2 ms. The display has a memory effect. When such electrophoretic particles are used for the variable iris according to the invention, power is only consumed when the particle positions are changed and the power consumption is very low. This is an important aspect for mobile applications.

Problems solved by technology

In contrast, for mechanical iris diaphragms the shape of the aperture is distorted if the size of the open aperture is very small, which leads to a change of the blur pattern.

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